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SAI International School
Class VII
Lesson Notes
Subject: Physics
Ch- Electric current and simple circuit
Subtopic: Electric Bell
USES OF AN ELECTROMAGNET:
i. Electromagnet is used in electric bell.
ii. Electromagnetic cranes are used to lift heavy loads.
iii. Magnetic materials can be separated from junk with the help of an electromagnet.
iv. Doctors use electromagnets to remove small pieces of magnetic materials that may have
accidentally fallen into the eyes.
ELECTRIC BELL:
An electric bell is a mechanical bell which functions on the principle of an ‘electromagnet or magnetic
effects of electric current’.
Construction of an electric bell:
i. An electric bell consists of a horseshoe type of electromagnet.
ii. The horseshoe electromagnet is connected to the source of current through a switch.
iii. There is an ‘armature’ a metallic gong and a hammer present in the electric bell.
iv. The iron strip present in the electric bell is attached to the gong through the contact screw.
v. The hammer is present near the electromagnet.
Working of an electric bell:
The switch is pressed and current flows through the circuit.
The electromagnet is powered and generates a magnetic field that attracts the iron strip towards
it.
The striker strikes the gong (bell).
When the striking arm strikes the gong, the contact is broken and current stops flowing through
the circuit.
This causes the electromagnet to lose its magnetic field.
